Electrochemical dechlorination promotes syngas production in N-heterocyclic carbene protected Au13 nanoclusters†

Abstract

Surface ligands play an important role in dictating the structure and catalytic properties of metal nanoclusters. Recently, a novel class of Au clusters protected by N-heterocyclic carbenes (NHCs) and halogens has been synthesized; however, the dynamic stability of the Au–NHCs/Au–halogen interface in real electrochemical environments as well as the influence of the ligand layer on the catalytic process remains obscure. Herein, we combined first-principles simulations with experiments to investigate the metal–ligand interface interaction of the classical [Au₁₃(NHC^Me)₉Cl₃]²⁺ cluster and its unique potential to promote electrocatalytic CO₂ reduction to syngas. Our simulations revealed the facile shedding of chlorine ligands from the surface of the Au₁₃ core upon electrochemical biasing, and the more negative the applied potential, the faster the kinetics of the Au–Cl bond cleavage. By contrast, the Au–NHC interface is highly stable, indicating the greater stability of Au–C bonds over the Au–Cl bonds under electrochemical conditions. Interestingly, the exposed icosahedral Au in dechlorinated [Au₁₃(NHC^Me)₉Cl₂]³⁺ cluster is capable of efficiently catalyzing electrochemical CO₂ reduction to generate CO and H₂ with comparable barriers in a wide potential range, showcasing its strong potential for syngas formation. Our predictions are further corroborated by experimental electrochemical data, where X-ray photoelectron spectroscopy (XPS) verified halogen stripping under acid or neutral media, and the activated Au₁₃ cluster demonstrated enhanced catalytic efficacy for syngas formation with a CO : H₂ ratio of approximately 0.8 to 1.2 across a broad potential range of −0.50 to −1.20 V. This work reveals an exciting frontier in the understanding of ligand etching dynamics in NHC-protected metal nanoclusters, and particularly, the catalytic preference for syngas production is revealed for the first time in gold-based nanoclusters, which is distinctive from previously reported Au nanoclusters that mainly produce CO.